Devices have been developed for cleaning the shaving head of a dry shaving apparatus. For example, German Patent No. DE 44 02 238 A1, which is incorporated herein by reference in its entirety, discloses, a receptacle configured for receiving the shaving head of a dry shaving apparatus. The receptacle is trough-shaped to conform to the contour of the shaving head and fully accommodates the shaving head. The receptacle has an outlet opening and an overflow which lead into a collecting container. The collecting container is connected by a return conduit to the reservoir containing the cleaning fluid. For this purpose the reservoir has a first opening into which the return conduit is inserted and sealed in place. At the beginning of the cleaning cycle the cleaning fluid is propelled by the motor-driven impelling device out of the reservoir through a second opening and by means of a conduit into the receptacle. During the cleaning cycle cleaning fluid is flushed through the receptacle continuously such that the quantity of cleaning fluid which is conveyed into the receptacle flows back through the return conduit into the reservoir.
At the beginning of the cleaning cycle, cleaning fluid is conveyed out of the reservoir into the receptacle. Little or no cleaning fluid flows back into the reservoir until the receptacle is filled as far as the overflow. Hence the fluid level in the reservoir drops. This lowering of the fluid level causes the volume of air in the reservoir to increase, as a result of which the pressure in the reservoir drops. As the pressure in the reservoir is lower than the atmospheric pressure, air flows in through the return conduit which connects the receptacle to the reservoir. Because the cleaning fluid did not completely fill the receptacle at the beginning of the cleaning cycle and during the initial period of the return of the cleaning fluid to the reservoir, the cross section of the return conduit was not completely closed by the returning cleaning fluid, the pressure difference between the reservoir and the surrounding atmosphere is compensated for by the influx of air through the return conduit. Air is admitted to the reservoir. After the receptacle has been filled, the quantity of cleaning fluid supplied to the receptacle flows through the return conduit into the reservoir. This leads, at the latest, after the impelling device is switched off, to a rise of the fluid level in the reservoir and to a corresponding reduction of the air volume, whereupon the air pressure in the reservoir increases to exceed ambient pressure. However, the returning cleaning fluid produces a fluid lock in the return conduit, thus preventing the air in the reservoir from escaping. The air is unable to overcome the resistance of the returning cleaning fluid and cannot escape from the reservoir until a sufficiently high pressure builds up in the reservoir. Accordingly, deaeration of the reservoir is hence delayed and the return of the cleaning fluid is obstructed by the escaping air. These brief interruptions to the return flow of the cleaning fluid result in brief fluid pileups in the receptacle, causing the fluid stream developing in the receptacle to be disturbed. This stream is important for discharging the hair particles dislodged from the shaving head. This disturbance of the fluid stream ultimately obstructs the discharge of hair residues from the receptacle. In some cases the abrupt deaeration of the reservoir is accompanied by noise which can disturb the user of the cleaning device.